Hacker News Reader

These things usually edit the HOSTS file, but this one proxies everything (including non-browser and https).

http://www.tekrevue.com/tip/edit-hosts-file-mac-os-x/ (or sudo nano /private/etc/hosts)

The primary way Focus blocks stuff is via an Automatic Proxy Configuration (PAC) file. It's located in System Preferences -> Network -> Advanced -> Proxies -> Automatic Proxy Configuration.

Maybe it edits the hosts file to block the sites or something, which would need the app to undo